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/* ----------------------------------------------------------------------- *
 *
 *   Copyright 2007-2009 H. Peter Anvin - All Rights Reserved
 *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 *   Boston MA 02110-1301, USA; either version 2 of the License, or
 *   (at your option) any later version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * rllpack.inc
 *
 * Very simple RLL compressor/decompressor, used to pack binary structures
 * together.
 *
 * Format of leading byte
 * 1-128	= x verbatim bytes follow
 * 129-223	= (x-126) times subsequent byte
 * 224-255	= (x-224)*256+(next byte) times the following byte
 * 0		= end of data
 *
 * These structures are stored *in reverse order* in high memory.
 * High memory pointers point to one byte beyond the end.
 */

#include <com32.h>
#include <stddef.h>
#include <string.h>

void rllpack(com32sys_t *regs)
{
	uint8_t *i = (uint8_t *)(regs->esi.l);
	uint8_t *o = (uint8_t *)(regs->edi.l);
	size_t cnt = regs->ecx.l;
	size_t run, vrun, tcnt;
	uint8_t *hdr = NULL;
	uint8_t c;

	vrun = (size_t)-1;
	while (cnt) {
		c = *i;

		run = 1;
		tcnt = (cnt > 8191) ? 8191 : cnt;
		while (run < tcnt && i[run] == c)
			run++;

		if (run < 3) {
			if (vrun >= 128) {
				hdr = --o;
				vrun = 0;
			}
			*--o = c;
			*hdr = ++vrun;
			i++;
			cnt--;
		} else {
			if (run < 224-126) {
				*--o = run+126;
			} else {
				o -= 2;
				*(uint16_t *)o = run + (224 << 8);
			}
			*--o = c;
			vrun = (size_t)-1;
			i += run;
			cnt -= run;
		}
	}
	*--o = 0;

	regs->esi.l = (size_t)i;
	regs->edi.l = (size_t)o;
}

void rllunpack(com32sys_t *regs)
{
	uint8_t *i = (uint8_t *)regs->esi.l;
	uint8_t *o = (uint8_t *)regs->edi.l;
	uint8_t c;
	size_t n;

	while ((c = *--i)) {
		if (c <= 128) {
			while (c--)
				*o++ = *--i;
		} else {
			if (c < 224)
				n = c - 126;
			else
				n = ((c-224) << 8) + *--i;
			c = *--i;
			while (n--)
				*o++ = c;
		}
	}

	regs->esi.l = (size_t)i;
	regs->ecx.l = (size_t)o - regs->edi.l;
	regs->edi.l = (size_t)o;
}